The invention relates to a method for producing a structured voluminous nonwoven comprising the following processing steps:
(a) manufacturing a spunbonded fabric consisting of a multitude of monofilaments that are stretched only at 50 to 70% of the maximum possible stretch range and are deposited as a fiber strand,
(b) pressing and welding the fiber strand into a raw nonwoven by using a first pair of rollers, and
(c) subsequently processing the raw nonwoven using a second pair of rollers, where at least one of the outer roller surfaces is made of metal and that consists of a positive roller with numerous projecting elements distributed across the outer surface of the roller, and of a negative roller with equally numerous recesses, where during the rolling process the projecting elements engage in the recesses and post-stretch the raw nonwoven in the area of the roller engagements.
The process described in the German Patent Application No. DE 195 47 319.1 is based on the state-of-the-art according to U.S. patent application Ser. No. 5,399,174. This U.S. patent describes a laminated foil where a nonwoven layer, which consists of crimped polymeric fiber bundles and is laminated with a polymeric foil, is embossed with the use of rollers such that a connecting and decorating pattern is created and connects the nonwoven with the foil. In the U.S. patent noted above, the section xe2x80x9cBACKGROUND OF THE INVENTIONxe2x80x9d also mentions that roller embossing is a kind of method that alters the feel of the nonwoven and at the same time adds a decorative design. Reference is made to the U.S. Pat. No. 4,592,943, among others, according to which a prior method is used, where the nonwoven is heated while the nonwoven foil to be processed passes through two grids such that the grid in its specific design is transmitted to the nonwoven and a corresponding image is formed. Additional reference is made to the U.S. Pat. No. 4,774,124, which discloses a pattern roller embossing method.
Also known, from the U.S. Pat. No. 5,356,364, is an embossing method, where unmatched male (positive) and female (negative) elements of two rollers provide an embossing process that is said to provide a particular fleeciness and embossing pattern.
Based on the teaching of the aforesaid German Patent Application 195 47 319.1, the objective of the present invention is to provide a spunbonded fabric, which has already been deposited and already exhibits partially bonded fibers and filaments corresponding to the nonwoven method, with a defined increase in volume, building upon the teaching of this patent application and improving it further.
Processing is carried out by using a second pair of rollers, where the outer surfaces of the rollers are made of metal, preferably both rollers of the same metal with a Rockwell Hardness (HRC) greater than 50, where the projecting elements of the positive roller are protrusions arranged in rows and where the surface of the negative roller exhibits axially extending ribs or xe2x80x9clamellasxe2x80x9d with recesses between them. With these axially arranged lamellas, which stretch across several protrusion distances, improved stretching of the 70% pre-stretched material can be achieved, in particular, a special structure that opens at the tip of the protrusions which, in the industry, is referred to as xe2x80x9capperturized nonwovenxe2x80x9d.
The openings are structured according to the geometry of the metal protrusions. In accordance with the amount of protrusions, one obtains a stronger opening and stronger perforation of the nonwoven. The openings have a shape turned out towards the back side of the nonwoven. On the usage side, the openings appear like delicate funnels that can also receive and transfer liquids. This effect is desired in a respective cover-stock material because liquids can be taken up and passed on. In addition, the three-dimensional structure that the nonwoven has assumed prevents the liquid from returning to the surface. The surface remains dry. In addition, the outside of the nonwoven has a soft, textile and pliable feel.
The fleeciness and the structure of the final product can largely be determined with the second pair of rollers. It is recommended to adjust the distance of the rollers of the second pair of rollers, thus adjusting the engagement of the rollers into one another. Preferably, the rollers used have a protrusion height of between 0.8 and 2 mm and the number of protrusions per 100 cm2 roller surface is selected between 2000 and 3000.
The temperature of the rollers is also important. For example, the process is carried out with the negative roller at a lower temperature than the positive roller. Examples of such temperatures for the positive roller are between 175xc2x0 C. and 190xc2x0 C. and for the negative roller only between 40xc2x0 C. and 80xc2x0 C.
To obtain a funnel-shaped structure of the nonwoven, it is recommended that the protrusions end in tips with the tips exhibiting, for example, the shape of onion towers, that is, they have a controlled shape that is first rounded and then ends in a tip. However, it is also possible to let the tips end as pyramid-shaped tips with an acute angle of 90xc2x120xc2x0.
Preferred initial materials for producing the nonwoven are polyethylene, polypropylene, polyesters or polyamide because these thermoplastics exhibit the desired fleeciness in a particularly pronounced manner.
Conventional methods are suitable as manufacturing methods for the nonwoven; for example, fabrics used as nonwovens are those manufactured by processes such as carding, airlaying or melt-blowing.
It is preferable to hold the raw nonwoven strand tight to the side at the roller edges during the second stretching such that it does not shrink. During the second stretching, that is, during the first run of the raw nonwoven strand through the second roller pair, the fabric is kept at a temperature that basically corresponds to the temperature that existed during the first stretching. The roller temperature, therefore, is maintained somewhat above and below this temperature.
The invention further relates to a pair of rollers, where the outer surfaces of the rollers are made of metal, where the male elements of the positive rollers are protrusions arranged in rows and where the surface of the negative roller exhibits lamella connectors in an axial direction with recesses between said lamellas such that during the rolling process the lamellas engage in the channels left open by the protrusions and where the length of the lamella connectors surpasses at least three protrusion distances.
For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings.